(a) Technical Field
The present invention relates to a sealing apparatus for a foam injection mold, and more particularly to a sealing apparatus that seals a foaming space between a core and a skin in a foam injection molding machine that manufactures a product having a foaming layer between the core and the skin to prevent leakage of a foaming liquid.
(b) Background Art
In general, crash pads that safely protect a passenger when the passenger collides due to an accident and the like are installed on front inner sides of a driver seat and a passenger seat as interior materials installed on a front side of an interior of a vehicle. Such a crash pad is manufactured to have an appealing surface in terms of external appearance while showing a resiliently cushioning performance and a property of absorbing an impact to some degree, by using a foam material.
Generally, a crash pad for a vehicle includes a skin which is a material that provides an appealing surface state, and a core operating as a frame of the crash pad on an inner side of the skin. A foam layer, such as a polypropylene (PP) foam layer, a polyurethane (PU) foam layer, and the like, that provide a cushioning performance and an impact absorbing performance is interposed between the skin and the base.
FIGS. 1A to 1D are exemplary views showing processes for manufacturing a crash pad according to the related art. A core 1 is formed through polymer injection molding, a skin 2 is formed through vacuum absorption, and a foam layer 3 is formed through foaming. The processes will be described below.
First, the core 1 is formed by injecting a polymeric resin material 1a into an injection mold including an upper mold 4 and a lower mold 5 (FIG. 1A), and the skin 2 separately preheated in a male vacuum-forming mold 6 is inserted into the injection mold to be formed through vacuum absorption (FIG. 1B). In particular, although not shown in the drawings, vacuum apertures that vacuum absorb the skin 2 are formed in the vacuum-forming mold 6, and the vacuum apertures are connected to one passageway in the mold, and then is connected to an external large capacity vacuum pump.
Further, after a foaming liquid 3a is injected into a core 1 of the lower mold 5, the foaming upper mold 7 to which the skin 2 is attached is closed and the skin 2 attached to the upper mold 7 is pressed and bonded onto the foaming liquid 3a of the lower mold 5. Thereafter, the skin 2 and an unnecessary marginal portion (e.g., a portion formed by the leaked foaming liquid and the like) of the foam layer 3 are cut off and removed together (e.g., trimmed), and a peripheral portion of the skin 2 is surrounded by the foam layer 3 and is bonded and fixed to the core 1 using an adhesive.
However, the manufacturing method according to the related art has the following problems.
First, since the core 1, the skin 2, and the foam layer 3 are formed separately in different molds, a total of three molds are required (e.g., core injecting-molding upper and lower molds, a vacuum-forming mold, and a foaming upper mold), which increases investment costs such as mold costs and manufacturing costs.
Further, since a peripheral portion of a cavity is opened when the lower mold 5 and the foaming upper mold 7 are closed, the foaming liquid may leak through the opened peripheral portion (e.g., an excessive loss of the foaming liquid and an increase in manufacturing costs may be caused).
Additionally, as shown in FIG. 1D, after the manufacturing process is completed, a separate process of separately cutting off a marginal portion formed by the solidified leaked liquid and a marginal portion of the skin 2 or cutting off only the leaked portion, surrounding the cut portion with a peripheral portion of the skin 2, and bonding the peripheral portion of the skin 2 to the cut portion is necessary.
Further, since the foaming liquid is injected into the opened cavity space (e.g., foaming space), a temperature of the injected foaming liquid must be controlled and maintained within a predetermined temperature range, which may be difficult.
In addition, a minimum thickness of the foaming layer 3 should be designed to be a predetermined thickness (e.g., 5 mm) or larger due to the solidification of the foaming liquid in a structure in which the foaming space is opened and the foaming liquid leaks, which may lower a degree of freedom of the crash pad.
Therefore, a molding apparatus has been developed in which a vacuum-forming mold and a foaming upper mold are integrated in the same mold and a peripheral portion of a skin may be attached to a core by a slider mold to seal a foaming space. The method reduces the number of molds, costs, and the cost price, solves an excessive loss of the foaming liquid, and improves a degree of freedom of design of the crash pad.
FIG. 2 is an exemplary schematic view showing a foam injection molding apparatus including a slider mold that prevents a leakage of a foaming liquid according to the related art, and a crash pad may be manufactured through IMG (In-Mold Grain) foam injection molding in the shown crash pad manufacturing apparatus. Specifically, an IMG foaming method refers to a method of forming an embossment on an inner surface of a mold (e.g., vacuum-forming mold) that forms a skin (e.g., formed of a Thermoplastic Olefin (TPO) material), and forms the skin through heating of the skin and suctioning of vacuum into a mold and forms an embossed shape on a surface of the skin.
As shown, the core 1 is formed by injecting a resin into a mold while the core injecting molds 10 and 11 are combined, and the skin 2 is vacuum-absorbed in the vacuum-forming mold 12 to be formed at the same time. Next, the mold is rotated and fed by an upper rotation unit to combine the vacuum-forming mold 12 in which the skin 2 is formed with the lower mold 11 in which the core 1 is formed, and then the foaming liquid is injected and foamed between the core 1 and the skin 2 to form the foam layer 3.
When the foaming liquid is injected, the slider mold 12a seals the foaming space by attaching a peripheral portion of the skin 2, and then the slider mold 12a moves forward by a distance suitable to form a seal during the foaming operation and then is fixed to maintain the seal. The slider mold 12a moves rearward to eject a product after the foaming operation.
Then, as shown in FIG. 3, the sealing operation is performed while a sealing boss 1c formed in the core 1 overlaps the skin 2, and thus preventing the foaming liquid from leaking to the exterior of the mold by the sealing boss 1c. The molding apparatus prevents leakage of a foaming liquid to some degree, and shares a mold, thereby reducing the number of molds, mold costs, invest costs, and the cost price.
However, to prevent leakage of the foaming liquid, an amount of the overlapping portion between the sealing boss 1c and the skin 2 should be maintained at a predetermined level (e.g., 0.3 mm) or higher and no gap should be generated between the sealing boss 1c and the skin 2. However, due to mold tolerances a and a′ and contractions b and c of materials indicated in FIG. 3, a gap may be generated between the sealing boss 1c and the skin 2. Accordingly, the foaming liquid leaks in the foaming process thereby, causing inconsistencies in the foaming pressure and foaming amount, and the leaked foaming liquid may be stuck to the mold, bonding the product to the mold, causing difficulty in ejecting the product.